… The 50 nations that today have troops operating in Afghanistan have collectively pledged to continue their mission well beyond 2014 and have drawn up a detailed concept of operations. But what remains under discussion is the size of the commitment.

Various options have been discussed, from the so-called "zero option" of complete withdrawal to a robust force of over 20,000 advocated publically by Generals John Allen and Jim Mattis, two key U.S. commanders.

After four years as the NATO supreme commander, and therefore overall strategic commander for operations in Afghanistan, I believe the correct number is about 9,000 U.S. and 6,000 allied troops, for a total of about 15,000 allied trainers who would focus on mentoring, training, and advising the 350,000 strong Afghan National Security Forces…